This video shows the subtle signs of autism from one child as he ages and his tremendous growth from years of therapy.
Of course, I have not included other behaviors such as tantrums, lack of social engagement, fear of strangers, covering of the ears and hyper-focus of behaviors. Other than two word basic needs sentences, he only spoke in movie quotes until the age of 5.
Those signs are obvious, however there are subtle signs that show themselves sometimes before the obvious behaviors present. The earlier a child is identified to need extra help the better the developmental outcome.
We never used medication, and did exclusively behavioral intervention with my son. We did modify to a healthier diet, with difficulty, but a cleaner food diet helped his overall health.